Technical Field
[0001] The present invention relates to a conveyor belt.
Background Art
[0002] Conveyor belts are used to convey various articles such as foods, metal parts, household
goods, and precision machines. There is suggested a belt in which a thermoplastic
synthetic resin layer is provided on both surfaces of a base part of plain weave,
and the surfaces are set to a predetermined state to enhance a sliding property (for
example, refer to PTL 1). In the belt described in PTL 1, a spherical substance is
mixed in a thermoplastic synthetic resin, and a part thereof is made to protrude from
the surface of the thermoplastic synthetic resin layer, thereby enhancing the sliding
property.
[0003] In addition, there is suggested a conveyor belt in which a cover layer made of a
high-adhesiveness thermoplastic resin is provided so that various objects to be conveyed
such as foods and plastic containers can be conveyed at a steep inclination (for example,
refer to PTL 2). In the belt described in PTL 2, the adhesiveness of the cover layer
is enhanced by adding a plasticizer to polyurethane (PU) or polyvinyl chloride (PVC),
thereby securing a high friction force.
Citation List
Patent Literature
Summary of the Invention
Technical Problem
[0005] A belt (elastic belt) having stretchability due to knitted fabric and elasticity
due to an elastic layer has sufficient strength, and can be used as an endless belt
without using a tension mechanism. The larger a coefficient of friction between a
conveying surface of a belt and an object to be conveyed, the more reliably convey
the object to be conveyed even in inclined conveyance. When increasing the coefficient
of friction of the conveying surface of the belt, hardness of the elastic layer decreases,
and this leads to a decrease in belt strength.
[0006] In this regard, an object of the invention is to provide a conveyor belt that has
sufficient stretchability and elasticity, and sufficient strength, and is capable
of reliably conveying an object to be conveyed even in inclined conveyance.
Solution to Problem
[0007] According to an aspect of the invention, there is provided a conveyor belt including:
a stretchable knitted fabric; an elastic layer that is provided on an upper surface
of the knitted fabric and is made of a first thermoplastic material; and a surface
resin layer that is provided on an upper surface of the elastic layer, is made of
a second thermoplastic material having hardness lower than hardness of the first thermoplastic
material, and the surface resin layer includes a conveying surface having unevenness.
Tensile strength of the conveyor belt is 3.5 to 35 MPa, and a coefficient of static
friction of the conveying surface is 0.5 to 1.0.
Advantageous Effects of the Invention
[0008] The conveyor belt of the invention includes the elastic layer that is laminated on
the stretchable knitted fabric and is made of a thermoplastic material, and thus the
tensile strength of the conveyor belt is 3.5 to 35 MPa, and has sufficient strength.
The surface resin layer provided on the upper surface of the elastic layer is made
of a thermoplastic material having hardness lower than that of the elastic layer,
and the surface resin layer includes the conveying surface having unevenness. According
to this, the coefficient of static friction of the conveying surface is defined to
0.5 to 1.0, and thus the conveyor belt of the invention can reliably convey an object
to be conveyed even in inclined conveyance.
Brief Description of the Drawings
[0009]
Fig. 1 is a cross-sectional view of a conveyor belt according to an embodiment in
a width direction.
Fig. 2 is a cross-sectional view of a conveyor belt of Modification Example A in a
width direction.
Fig. 3 is a cross-sectional view of a conveyor belt of Modification Example B in a
width direction.
Description of Embodiments
[0010] Hereinafter, an embodiment of the invention will be described in detail with reference
to the accompanying drawings.
1. Overall Configuration
[0011] A conveyor belt 10 illustrated in Fig. 1 includes a core body layer 12, and a surface
resin layer 20 provided on a surface of the core body layer 12. The core body layer
12 has a laminated structure including a stretchable knitted fabric 15, and an elastic
layer 14 that is provided on the knitted fabric 15 and is made of a first thermoplastic
material. The surface resin layer 20 is made of a second thermoplastic material having
hardness lower than that of the first thermoplastic material, and the surface resin
layer 20 includes a conveying surface 21 having unevenness including a plurality of
vertical grooves 22.
<Knitted Fabric>
[0012] The knitted fabric 15 imparts stretchability to the conveyor belt 10. The knitted
fabric 15 is not particularly limited as long as the knitted fabric 15 is obtained
by knitting fibers. A knitted fabric that is typically used in an elastic belt can
be used as the knitted fabric 15 in the conveyor belt 10. A method of knitting the
knitted fabric 15 may be either wrap knitting or weft knitting. Fibers forming the
knitted fabric 15 can be selected, for example, from a polyester fiber, a nylon fiber,
an aramid fiber, a glass fiber, and a cotton yarn, and the like. The fibers used in
the knitted fabric 15 may be used alone or may include two or more different kinds.
[0013] The thickness of the fibers forming the knitted fabric 15 is not particularly limited,
and is approximately 20 to 280 T (decitex) as an example. It is preferable that the
thickness of the knitted fabric 15 is approximately 0.3 to 0.8 mm, and more preferably
approximately 0.4 to 0.6 mm.
<Elastic Layer>
[0014] The elastic layer 14 is made of the first thermoplastic material, and imparts flexibility
and strength to the conveyor belt 10. Examples of the first thermoplastic material
include thermoplastic elastomers made of polyurethane, polyolefin such as polyethylene/polypropylene,
and polyester. The polyurethane elastomers are particularly preferable from the viewpoint
of excellent processability and high strength. It is preferable that the thickness
of the elastic layer 14 is approximately 0.2 to 1.5 mm, and more preferably approximately
0.3 to 0.8 mm
<Surface Resin Layer>
[0015] The surface resin layer 20 is constituted by the second thermoplastic material having
hardness lower than that of the first thermoplastic material. In addition, the surface
resin layer 20 has unevenness in the conveying surface 21. Since the surface resin
layer 20 is constituted by the thermoplastic material, the surface resin layer 20
has excellent abrasion resistance. For example, the second thermoplastic material
may be a mixture of the first thermoplastic material and an additive to be described
later. It is preferable that the thickness of the surface resin layer 20 is approximately
0.2 to 1.5 mm, and more preferably approximately 0.3 to 0.8 mm. The thickness of the
surface resin layer 20 represents a maximum thickness in a convex part of the unevenness.
[0016] The unevenness of the conveying surface 21 in this embodiment includes the plurality
of vertical grooves 22 along a longitudinal direction of the surface resin layer 20.
In the vertical grooves 22, a width w is approximately 0.5 to 3.0 mm, and a depth
d is approximately 0.2 to 1.0 mm. The vertical grooves 22 are provided at the entire
region of the conveying surface 21 in a width direction of the surface resin layer
20, and thus the unevenness exists at the entire region of the conveying surface 21.
[0017] Tensile strength of the surface resin layer 20 is 3.5 to 8 MPa. When the tensile
strength of the surface resin layer 20 is 3.5 MPa or more, the conveyor belt 10 can
be used in a typical conveyance use without any problem. The tensile strength of the
conveyor belt 10 is defined to 3.5 to 35 MPa in consideration of a highly stretchable
characteristic of the belt. Since the conveyor belt 10 includes the stretchable knitted
fabric 15 and the elastic layer 14 made of the thermoplastic material as described
above, a predetermined range of tensile strength is secured. It is preferable that
the tensile strength of the conveyor belt 10 is 10 MPa or more, and more preferably
20 MPa or more.
[0018] In addition, in the conveyor belt 10, a coefficient of static friction of the conveying
surface 21 of the surface resin layer 20 is 0.5 to 1.0. Since the surface resin layer
20 is constituted by a predetermined second thermoplastic material and the unevenness
is provided in the conveying surface 21, the coefficient of static friction in a predetermined
range is secured. When the coefficient of static friction of the conveying surface
21 is 0.5 or more, it is possible to reliably convey an object to be conveyed even
in a case where the conveyor belt 10 is provided at an inclination. In the conveyor
belt 10, the upper limit of the coefficient of static friction is defined to 1.0 in
consideration of a characteristic of a high coefficient of friction for article conveyance.
It is preferable that the coefficient of static friction is 0.6 or more, and more
preferably 0.7 or more. A method for obtaining the tensile strength and the coefficient
of static friction will be described in detail later.
2. Manufacturing Method
[0019] The conveyor belt 10 can be manufactured by an arbitrary method as long as the knitted
fabric 15 and the elastic layer 14 are fixed to each other, and the elastic layer
14 and the surface resin layer 20 are fixed to each other, and thus peeling-off does
not occur.
[0020] First, a thermoplastic sheet serving as the elastic layer 14 is prepared by using
a predetermined thermoplastic elastomer with a calendar device or an extrusion device.
The size of the sheet is adjusted to the size of the stretchable knitted fabric 15.
The sheet can be fixed to the knitted fabric 15 by using rubber paste.
[0021] The stretchable knitted fabric 15 is impregnated with the rubber paste in advance.
The rubber paste can be impregnated into the knitted fabric 15 by using an application
unit such as a coater and a brush. Alternatively, the knitted fabric 15 may be immersed
in the rubber paste to impregnate the knitted fabric 15 with the rubber paste.
[0022] The elastic layer 14 is placed on the knitted fabric 15 impregnated with the rubber
paste, and both the elastic layer 14 and the knitted fabric 15 are fixed to each other
under a heating and pressurizing condition. In this manner, the core body layer 12
in which the elastic layer 14 made of the first thermoplastic material is laminated
on the stretchable knitted fabric 15 is obtained. The core body layer 12 contributes
to the tensile strength of the conveyor belt 10. The tensile strength can be changed
in a range of 3.5 to 35 MPa by adjusting a ratio between the elastic layer 14 and
the knitted fabric 15 in the core body layer 12. For example, as the ratio of the
elastic layer 14 increases, the tensile strength tends to increase.
[0023] On the other hand, the surface resin layer 20 made of the second thermoplastic material
is prepared by using a predetermined raw material composition. For example, the raw
material composition can be prepared by mixing an ether-based thermoplastic polyurethane
elastomer (hereinafter, referred to as "ether-based TPU") as the first thermoplastic
material, a hydrogenated styrene-based thermoplastic elastomer (hereinafter, referred
to as "styrene-based TPE) as an additive, a compatibilizer and wax. When using the
raw material composition, the second thermoplastic material having hardness lower
than that of the first thermoplastic material is obtained.
[0024] For example, ratios of respective components in the raw material composition can
be set as follows.
Ether-based TPU: 50% by mass to 60% by mass
Styrene-based TPE: 10% by mass to 30% by mass
Compatibilizer: 0% by mass to 10% by mass
Wax: 5% by mass to 15% by mass
Calcium carbonate: 0% by mass to 25% by mass
[0025] An arbitrary component may be blended as necessary to prepare the raw material composition.
[0026] As the ether-based TPU, for example, an ether-based thermoplastic urethane resin
having hardness equivalent to 80 measured by a type A durometer in accordance with
Japanese Industrial Standard JIS K6253 can be used. As the compatibilizer, a mixture
of a hydrogenated styrene-based elastomer and a thermoplastic urethane resin can be
used. As the wax, a commercially available solid paraffin oil can be used.
[0027] A resin sheet serving as the surface resin layer 20 is prepared by using the raw
material composition prepared by blending respective components in a predetermined
ratio with a calendar device. That is, two rolls disposed at a predetermined interval
are rotated in the same direction while flowing the raw material composition in a
molten state between the two rolls to obtain a band-shaped resin sheet. At this time,
one roll is set to a roll having a smooth surface, and the other roll is set to a
roll including convex parts corresponding to the vertical grooves, thereby a resin
sheet including the vertical grooves is obtained. The size of the resin sheet is adjusted
to the size of the stretchable knitted fabric 15.
[0028] The obtained resin sheet is disposed on the elastic layer 14 in the core body layer
12 prepared in advance to obtain a laminated body. The laminated body is laminated
during extrusion, or is heated and compressed after sheet formation to be processed
into a predetermined thickness. For example, the thickness of the laminated body after
heating and compression can be set to approximately 1.0 to 3.0 mm. When performing
the heating and compression, the elastic layer 14 and the surface resin layer 20 in
the core body layer 12 are fixed to each other.
[0029] As described above, the conveyor belt 10 according to this embodiment in which the
surface resin layer 20 is laminated on the core body layer 12 including the knitted
fabric 15 and the elastic layer 14 is obtained. The conveyor belt 10 can be applied
to an inclined conveyor or the like by joining both end parts by a finger joint to
be processed into an endless shape.
[0030] The coefficient of static friction of the conveying surface 21 of the surface resin
layer 20 depends on the hardness of the second thermoplastic material that constitutes
the surface resin layer 20. It is possible to change the coefficient of static friction
of the conveying surface 21 in a range of 0.5 to 1.0 by adjusting a blending ratio
of respective components in the raw material composition. For example, in the raw
material composition, as the ratio of the styrene-based TPE to the ether-based TPU
is larger, the coefficient of static friction increases.
[0031] Alternatively, it is also possible to change the coefficient of static friction of
the conveying surface 21 by adjusting dimensions (the width w and the depth d) of
the vertical grooves 22 provided in the conveying surface 21 of the surface resin
layer 20. For example, as the width w or the depth d of the vertical grooves 22 is
larger, dust or dirt is less likely to be accumulated on the surface of the conveying
surface 21, and thus the coefficient of static friction increases.
3. Operation and Effect
[0032] The conveyor belt 10 according to this embodiment includes the stretchable knitted
fabric 15 and the elastic layer 14 that is provided on the knitted fabric 15 and is
made of a thermoplastic material. Since the conveyor belt 10 has stretchability, the
conveyor belt 10 can be used as an endless belt without using a tension mechanism.
Furthermore, since the conveyor belt 10 includes the knitted fabric 15 and the elastic
layer 14, the conveyor belt 10 has sufficient strength and the tensile strength thereof
is 3.5 to 35 MPa.
[0033] The surface resin layer 20 provided on the elastic layer 14 includes the conveying
surface 21 that is constituted by a thermoplastic material having hardness lower than
that of the elastic layer 14, and has unevenness. As is typically known, in the thermoplastic
material, when the hardness decreases, the coefficient of friction increases. Accordingly,
the conveying surface 21 of the surface resin layer 20 has a coefficient of static
friction larger than that of the surface of the elastic layer 14. The conveying surface
21 has the coefficient of static friction in a range of 0.5 to 1.0. The conveyor belt
10 according to this embodiment can reliably convey an object to be conveyed even
in inclined conveyance, and sufficient abrasion resistance is also provided.
[0034] The conveyor belt 10 can be appropriately used for an inclined conveyor or a gap
adjustment conveyor. In this case, the object to be conveyed can be moved in an upper
and lower direction while being moved in a horizontal direction, and thus this leads
to space saving of an installation location or a working region. In addition, an object
to be conveyed (for example, a small-sized object to be conveyed, or the like), which
is difficult to be stably conveyed in a case where the conveyor belt 10 is provided
to cover rollers in a roller conveyor, can be stably conveyed.
4. Examples
[0035] Hereinafter, the conveyor belt of the invention will be described in detail with
reference to specific examples, but the invention is not limited to the following
specific examples.
<Example>
[0036] First, a urethane rubber sheet (thickness: 0.3 mm) was prepared by using the ether-based
TPU with an extrusion device. The urethane rubber sheet serves as an elastic layer
of the conveyor belt.
[0037] A stretchable knitted fabric was applied with rubber paste (application amount: 5
g/m
2). The knitted fabric applied with the rubber paste and the ether-based TPU were compressed
during extrusion molding to fix both the knitted fabric and the ether-based TPU, thereby
obtaining a core body layer.
[0038] The following components were blended in the following prescription to prepare the
raw material composition of the surface resin layer.
Ether-based TPU (hardness: 80°): 65% by mass (433 parts)
Styrene-based TPE (hardness: 55°): 15% by mass (100 parts)
Compatibilizer: 5% by mass (5 parts)
Wax (solid paraffin oil): 15% by mass (100 parts)
[0039] A resin sheet (width: 1000 mm, and thickness: 0.3 mm) was prepared by using the obtained
raw material composition with the extrusion device as described above. A plurality
of vertical grooves (width: 0.5 mm, and depth: 0.4 mm) along a longitudinal direction
were formed in a surface of the resin sheet. The resin sheet serves as a surface resin
layer of the conveyor belt.
[0040] Respective layers were compressed during extrusion molding to obtain the conveyor
belt of the example. The thickness of the conveyor belt is 2.3 mm.
<Comparative Example>
[0041] A conveyor belt of a comparative example was obtained by using only the core body
layer prepared in the above-described example.
[0042] The tensile strength and the coefficient of static friction were measured with respect
to the conveyor belts of the example and the comparative example. A test method is
as follows.
<Tensile Strength>
[0043] The tensile strength is obtained in accordance with JIS K6301 (New JIS K6251). The
conveyor belts of the example and the comparative example are set to a dumbbell-shaped
specimen (No. 3), and are pulled until being fractured at a speed of 500 mm/min by
using a tensile tester (manufactured by SHIMADZU CORPORATION) under an environment
of a temperature of 23°C and relative humidity of 50%. The tensile strength is calculated
from the maximum tensile force necessary for fracture of the specimen.
<Coefficient of Static Friction>
[0044] The coefficient of static friction is measured by a surface property measuring device
(manufactured by Shinto Scientific Co., Ltd.). The conveyor belt of the example and
the comparative example are used as a specimen having dimensions of 20 mm × 30 mm,
and a cardboard is used as an object. Each of the specimens is placed on the cardboard,
and the specimen is moved at a speed of 5 mm/min while applying a load of 0.8 kPa
to obtain the coefficient of static friction.
[0045] The tensile strength of the conveyor belt of the example was 4.6 MPa, and the tensile
strength of the conveyor belt of the comparative example was 4.8 MPa. Even when the
surface resin layer is provided on a surface of the core body layer (conveyor belt
of the comparative example), the tensile strength of the core body layer is not damaged,
and is maintained to 95% or more. It can be seen that the conveyor belt of the example
has sufficient tensile strength.
[0046] The coefficient of static friction of the conveyor belt of the example was 0.95,
and the coefficient of static friction of the conveyor belt of the comparative example
was 0.45. The coefficient of static friction of a surface of the belt of the example
is two or more times that of the belt of the comparative example.
5. Modification Example
[0047] The invention is not limited to the embodiment described here, and can be appropriately
modified in a range not departing from the gist of the invention.
[0048] In the above-described embodiment, the unevenness including the plurality of vertical
grooves 22 is provided in the entire region of the surface resin layer 20 in the width
direction, but there is no limitation thereto. The coefficient of static friction
can be increased as long as the unevenness is provided at least at 50% of the conveying
surface 21 of the surface resin layer 20 in the width direction.
[0049] The plurality of vertical grooves 22 may be formed when preparing the surface resin
layer 20. For example, a sheet-shaped material is prepared on release paper by using
a raw material composition, and a pressurizing member having a surface shape corresponding
to the vertical grooves is disposed on the sheet-shaped material. The sheet-shaped
material interposed between the release paper and the pressurizing member is solidified
by a typical method.
[0050] The release paper is removed, the sheet-shaped material is disposed on the elastic
layer 14 in the core body layer 12 that is prepared in advance, thereby obtaining
a laminated body. An upper surface of the laminated body serves as a pressurizing
member, and a lower surface serves as the stretchable knitted fabric 15. The laminated
body is heated and compressed to be processed into a predetermined thickness. For
example, the thickness of the laminated body after heating and compression may be
set to approximately 1 to 3 mm. When performing heating and compression, the elastic
layer 14 in the core body layer 12 and the surface resin layer 20 are fixed to each
other, thereby obtaining the conveyor belt of the embodiment.
[0051] With regard to the unevenness of the conveying surface 21, a concave part and a convex
part can be alternately provided in vertical and horizontal directions. A pitch of
the unevenness provided in the vertical and horizontal directions can be set, for
example, to approximately 0.5 to 3.0 mm, and the height of the convex part of the
unevenness can be set, for example, to approximately 0.2 to 1.0 mm. To provide the
unevenness, a canvas for weight processing having a predetermined unevenness may be
used when preparing the surface resin layer 20.
[0052] In the above-described embodiment, the core body layer 12 is set to a laminated structure
of the stretchable knitted fabric 15 and the elastic layer 14, but there is no limitation
thereto. For example, as in a core body layer 12A in a conveyor belt 10A in Fig. 2,
an additional elastic layer 16 made of a thermoplastic material can be provided on
a lower surface of the knitted fabric 15 (Modification Example A). The thermoplastic
material used in the additional elastic layer 16 may be the same as or different from
the thermoplastic material used in the elastic layer 14.
[0053] As in a core body layer 12B in a conveyor belt 10B in Fig. 3, an additional stretchable
knitted fabric 17 may be provided on a lower surface of the additional elastic layer
16 (Modification Example B). Fibers of the additional knitted fabric 17 and a method
for knitting the additional knitted fabric 17 may be the same as or different from
those in the knitted fabric 15.
[0054] The second thermoplastic material is not limited to the mixture of the first thermoplastic
material and the additive, and may be a mixture of a thermoplastic material different
from the first thermoplastic material and the additive.
Reference Signs List
[0055]
- 10, 10A, 10B
- Conveyor belt
- 12, 12A, 12B
- Core body layer
- 14
- Elastic layer
- 15
- Knitted fabric
- 16
- Additional elastic layer
- 17
- Additional knitted fabric
- 20
- Surface resin layer
- 21
- Conveying surface
- 22
- Vertical groove